Recharger for hydrogen fuel cells

ABSTRACT

A recharger includes a manifold having an input to couple to a hydrogen generating module and an output port to couple to at least one rechargeable fuel cell. A vacuum pump is coupled to the manifold to evacuate the manifold. A valve is coupled to the manifold between the vacuum pump and the input of the manifold. A controller is coupled to control the vacuum pump and the valve, as well as an optional fan.

RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 61/159,254 (entitled Lightweight Recharger for Hydrogen Fuel Cells,filed Mar. 11, 2009) which is incorporated herein by reference.

BACKGROUND

State of the art primary batteries do not provide adequate run time inportable electronic devices. Soldiers typically carry several pounds ofbatteries per day in the field, which on multi-day missions becomes asubstantial portion of their total load. The US Army plans to transitionfrom using individual batteries in each device the soldier carries, tolarger, higher-power central power sources which would take advantage ofthe superior energy density and specific energy of larger fuel cellbased power sources. This transition will not happen immediately, and inthe mean time, better, longer lasting “batteries” are desired to easethe burden on the soldier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a recharging system for hydrogen fuel cellgenerators according to an example embodiment.

FIG. 2 is a block diagram of a replaceable fuel source module accordingto an example embodiment.

FIG. 3 is a block diagram illustration showing further details of therecharger according to an example embodiment.

FIG. 4 is a block diagram of a rechargeable fuel cell according to anexample embodiment.

FIG. 5 is a flow chart diagram of a charging process according to anexample embodiment.

FIG. 6 is a flow chart representation of a further process for chargingrechargeable fuel cells according to an example embodiment.

FIG. 7 is a block diagram of an alternative fuel cell rechargeraccording to an example embodiment.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description of example embodiments is,therefore, not to be taken in a limited sense, and the scope of thepresent invention is defined by the appended claims.

In one embodiment, a recharging system 100 is illustrated in blockdiagram form in FIG. 1 consists of a central hydrogen fuel cellrecharger 105, and rechargeable fuel cells 110 in the form factors ofprimary alkaline and lithium batteries. Recharging system 100 in oneembodiment provides a power solution in one embodiment, providing a highenergy density system for recharging batteries. The rechargeable fuelcells 110 provide three to five times the energy density and run time ofcurrent alkaline and lithium batteries, but instead of being discardedat the end of life, they can be recharged with hydrogen by therecharger.

Use of the recharger 105 in conjunction with rechargeable fuel cells 110may provide a power solution with dramatically improved run time,reduced weight, and lower cost. In one embodiment, a chemical hydridefuel source 115 such as LiAlH4 reacts spontaneously with water togenerate hydrogen. The fuel source 115 in one embodiment includesmultiple fuel rods 120. Ambient air with some level of humidity containswater vapor, and is circulated over fuel rods 120 via an ambient airinlet 122. A dry air outlet 123 may be used to provide an outlet for airthat has passed over the fuel rods 120. Together, the ambient air inlet122 may be positioned at one end of the fuel rods, with the dry airoutlet 123 positioned at a second end of the fuel rods 120, to promoteflow of humid air over the fuel rods. An optional fan 124 may be used ateither the inlet 122 or outlet 123 to further promote such flow.

The fuel rods 120 are packed together in one embodiment, such thatchannels 125 are disposed between the fuel rods 120. The fuel rods 120may include a LiAlH4 core, with a selectively permeable membrane (SPM)shell 130 that may surround each entire fuel rod, or a group of fuelrods in further embodiments. The fuel rods 120 may have a gasimpermeable cap 135 on an end of the fuel rods that are closest to theambient air inlet 122. The SPM shell 130 allows water vapor diffusionbut prevents hydrogen diffusion. Water vapor from the humid air diffusesthrough the SMP shell 130 and reacts with the LIALH4, generatinghydrogen. In further embodiments, fuel source 115 may be formed as asolid block with channels to disperse the humid air throughout the fuelsource 115.

The generated hydrogen flows out the bottom of the fuel source 115, suchas fuel rods 120 into an input manifold 140, which is coupled to ahydrogen pump 145. An outlet 147 of the hydrogen pump 145 is coupled toan output manifold 150 which has individual gas carrying connections toeach rechargeable fuel cell 110. A vacuum pump 155 may also be connectedto the manifold 150 and hence to the fuel cells 110, and is used toevacuate the fuel cells 110 and test their integrity. In one embodiment,the fuel cells are evacuated to a pressure below 1 torr. Evacuation isdone to remove gases (oxygen, water vapor, nitrogen, and left overhydrogen) that might cause problems with operation of the fuel cell.

Hydrogen from the fuel rods 120 is pumped into the fuel cells 110 viathe manifolds 140, 150, and hydrogen pump 145, to refill or rechargethem with hydrogen. Control electronics 160, which may be powered by aseparate fuel cell 165, manages the vacuum and hydrogen pumps, as wellas an optional fan 124. The separate fuel cell 165 may also be used toprovide power to the pumps and fan and other elements that may requirepower, such as various valves to aid in performing recharging operationsdescribed below. In one embodiment, the separate fuel cell 165 iscoupled to the manifold 140 via a gas line 170.

An example replaceable fuel source module 210 is shown in block diagramform in FIG. 2. The module 210 may include one or more fuel rods orother source of water released hydrogen as described above, It may betransported with a cover 215 to block ambient air from reaching the fuelrods until the module is ready for use to generate hydrogen. The module210 includes a hydrogen outlet port 220 that includes a valve 225 toprevent ambient air from reaching the fuel rods. The port 220 may matewith the manifold 140 in FIG. 1. The valve 225 may be automaticallyopened by insertion of the port 220 into the manifold 140 in oneembodiment, or may be controlled by electronics 160 in variousembodiments. A dry air outlet cover 230 may be used to cover the dry airoutlet and to prevent ambient from reaching the fuel rods. The cover 230may be removed when the module 210 is to be used to generate hydrogenduring recharging processes. In some embodiments, the module 210 may beremoved after a recharging process, and the covers 215 and 230 replaced,to store the module 210 between uses. In further embodiments, covers 215and 230 include valves that may be actuated via electronics 160 inrecharger 105 when module 210 is coupled to the recharger 105.

FIG. 3 is a block diagram illustration showing further details of therecharger 105, with reference numbers consistent with those used inFIG. 1. Recharger 105 includes a portion of manifold 140, and may alsoinclude a valve 310 operating under control of electronics 160 in oneembodiment. Valve 140 may be used to stop hydrogen flow, and seal offthe portion of manifold 140 in recharger 105 from the fuel source.Outlet 147 is coupled via a valve 310 to the vacuum pump 155. The valve310 may be coupled at the point outlet port 147 couples to manifold 150,and may be controlled by electronics 160 to regulate flow between vacuumpump 155, hydrogen pump 145 and manifold 150. A pressure sensor 320 iscoupled to manifold 150 to measure pressure in manifold 150 at selectedtimes during a recharging process. A further fuel cell valve 325 may beincluded in each path to a fuel cell to be recharged in one embodiment.The fuel cell valves 325 may be used to select individual fuel cells tothe manifold in a controlled manner. Using pressure sensor 320 andvalves 315 and 325, each individual fuel cell may be vacuum tested fordamage, or individually measured to determine if they are full ofhydrogen.

In a further embodiment, fuel cell 165 may be coupled to a rechargeablebattery 330. The rechargeable battery may be a standard battery thatretains charge over an extended period of time, and provides a backuppower source for electronics 160 and the assorted fans, pumps and valvesin various embodiments. Battery 220 may be charged via the fuel cell 165generating electricity when it is supplied hydrogen. Battery 220 maythen be used to power the electronics during a recharging process priorto fuel cell 165 receiving hydrogen. It may also be used as a backuppower source should fuel cell 165 become inoperative. It should be notedthat while electronics 160 is shown as a single module, the functions itperforms may be distributed in any desired manner throughout the system.In still further embodiments, a regular battery 220 may be used, or therecharger 105 may be adapted to plug into an external power source, suchas a power outlet coupled to the power grid or an automobile lighterreceptacle.

FIG. 4 illustrates a rechargeable fuel cell 110 in further detail. Inone embodiment, the fuel cell 110 is in the shape of an AA battery formfactor, having a cathode 410 and an anode 420. In one embodiment, theanode 420 end of the fuel cell 110 includes a valve 430, that uponinserting of the fuel cell into the recharger 105, the valve 430 mateswith the manifold 150, causing the valve 430 to open and allow hydrogento flow into the fuel cell 110 and be absorbed.

A simple charging process is indicated in flow chart form at 500 in FIG.5. The process may be performed by a combination of human interactionsand recharger processing in various embodiments. At 510, one or morefuel cells may be inserted such that they are coupled to the manifold150 in a sealed manner. The vacuum pump 155 may be used to evacuate themanifold 150 and the cells. The valves may be controlled in a manner tofacilitate such evacuation. In one embodiment, the pressure sensor maybe used to determine if one or more fuel cells has failed, or if therecharger 105 is otherwise leaking. The cells may be individually testedfor leaks in a further embodiment using the valves to isolate them. At520, hydrogen generation is performed and the hydrogen is pumped intomanifold 150. The cells absorb the hydrogen as indicated at 540. Uponcompletion of charging, the cell may be removed, and hydrogen generationand pumping stopped.

FIG. 6 is a flow chart representation of a further process 600 forcharging rechargeable fuel cells. Once one or more fuel cells have beencoupled to manifold 150, hydrogen may be pumped into the fuel cells.Pressure in manifold 150 may then be measured at 620, with pumpingstopped at 630 when the pressure reaches a first threshold. The firstthreshold may be a predetermined pressure that is consistent with adesired level of charging a particular type of rechargeable fuel cell.Some hydrides may utilize a higher pressure, which varies from a few PSIabove atmosphere to one hundred of more PSI. At 640, after a desireddelay time, the pressure is measured again. If more hydrogen has beenabsorbed, the pressure may have dropped from the first threshold. Asecond threshold, selected to indicate that the fuel cell may not befully charged, is used to determine at 650 whether to pump hydrogenagain at 610 and repeat the process until the pressure does not drop tothe second threshold after a predetermined amount of time.

In an alternative embodiment as illustrated in a simplified blockdiagram in FIG. 7, a hydrogen stream 710 containing water vapor iscirculated via a pump or fan 715 through an arrangement of LiAlH4 fuelrods 720. The fuel rods 720 react with the water vapor in the hydrogenstream 710, producing more hydrogen. Once dried by the fuel rods, thehydrogen 723 is passed by a “water exchanger” which consists of watervapor/hydrogen selectively permeable membranes 725 (membranes such asNafion® may be suitable), which allow water vapor from ambient air topermeate the membrane into the hydrogen stream, without losingsubstantial amounts of hydrogen. A fan 730 may be used to circulatehumid ambient air over the air side of the “water exchanger”. A hydrogenpermeable, water impermeable membrane 735 may be used at an inlet to thewater exchanger 725 to prevent water from reaching the hydrogen 723.Hydrogen 723 produced by the hydrogen generator may be fed through anoutlet port 735 and attached directly to a rechargeable fuel cell 740. Apump 745 may be used to control the pressure of hydrogen fed to the fuelcell 740. A vacuum pump 750 may be used to remove contaminant gases suchas water vapor or oxygen from the fuel cell 740 prior to filling withhydrogen. The fuel cell 740 may be held by a heat sink 755 duringrecharging to remove the heat generated during refueling, resulting in amore rapid refueling process.

In a further embodiment, a fuel cell 760 is coupled to receive hydrogenproduced by the hydrogen generator and provide power to one or more ofthe pumps, fans and control electronics. The fuel cell may be separatefrom the rechargeable fuel cells supported in a manifold 765, and neednot have a separate hydrogen producing fuel. It may receive hydrogendirectly from the hydrogen generate to generate the power. In oneembodiment, it may be located prior to a hydrogen pump in the manifold,or located within a fuel container proximate the rods, but coupled toreceive hydrogen via conduits from the fuel rods coupled to the outletport and to receive oxygen to react with the hydrogen.

Alternately, the fuel could be arranged in a series of fins as on a heatexchanger, where the selectively permeable membrane acts as the surfaceof the fin, creating a large surface area for passive transport of watervapor from the surrounding air into the hydrogen generator. The hydrogengenerator then produces hydrogen at a pressure greater than atmosphericpressure. In this way the hydrogen generator could be entirely passive,consuming no electrical power. Hydrogen at the pressure inside thehydrogen generator would be fed directly into the fuel cell.

The Abstract is provided to comply with 37 C.F.R. § 1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

The invention claimed is:
 1. A recharger comprising: a fuel containerhaving multiple fuel rods and a humid air inlet, wherein the fuel rodsare disposed in selectively permeable membranes, wherein the fuelcontainer has an outlet that provides hydrogen generated from the fuelrods to recharge multiple removable hydrogen-rechargeable powergenerators, and wherein the multiple removable hydrogen-rechargeablepower generators each has its own hydrogen storage and has a shapecorresponding to a form factor of primary alkaline or lithium batteries;a manifold attached to the outlet, wherein the manifold includesmultiple output ports to receive the multiple removablehydrogen-rechargeable power generators and to distribute the hydrogenfor storage in the multiple removable hydrogen-rechargeable powergenerators, wherein each output port includes an independently actuatedvalve; a hydrogen pump coupled to the manifold to provide pressurizedhydrogen to the removable hydrogen-rechargeable power generators; avacuum pump coupled to the manifold and adapted to remove air from themultiple removable hydrogen-rechargeable power generators prior toproviding hydrogen to the removable hydrogen-rechargeable powergenerators; control electronics adapted to control the hydrogen pump, tocontrol the vacuum pump, and to control each independently actuatedvalve within the manifold; and an internal fuel cell coupled to receivegenerated hydrogen and provide power to the control electronics, thehydrogen pump, the vacuum pump, and a fan.
 2. The recharger of claim 1,wherein the hydrogen pump is coupled to the manifold to providepressurized hydrogen to the multiple removable hydrogen-rechargeablepower generators.
 3. The recharger of claim 2, wherein the vacuum pumpis coupled to the manifold and adapted to remove air from the manifoldprior to the hydrogen pump providing hydrogen to the multiple removablehydrogen-rechargeable power generators.
 4. The recharger of claim 3,wherein the control electronics are adapted to control the hydrogen pumpand vacuum pump.
 5. The recharger of claim 1 wherein the fuel rodscomprise chemical hydride fuel rods, and wherein the humid air inlet ispositioned to receive ambient humid air.
 6. The recharger of claim 1wherein the fuel container further comprises a fan positioned to drawhumid air in the humid air inlet, pass the humid air by the fuel rods,and vent dry air via an air outlet in the fuel container.
 7. Therecharger of claim 1 wherein the fuel rods are arranged in a series offins.
 8. The recharger of claim 7 wherein the fuel rods produce hydrogenat pressure.
 9. The recharger of claim 7 wherein the fins create a largesurface area for passive transport of water vapor from the surroundingair past the fins.
 10. The recharger of claim 1 wherein the fuel rodscomprise LiAlH4.
 11. The recharger of claim 1 wherein the manifoldcomprises at least one heat sink for each hydrogen-rechargeable powergenerator.
 12. A recharger comprising: a power generator manifoldincluding: an input to attach to a hydrogen generating module; andmultiple output ports shaped to receive multiple removablehydrogen-rechargeable power generators and to distribute hydrogen forstorage in the multiple removable hydrogen-rechargeable powergenerators, each output port including an independently actuated powergenerator manifold valve; wherein the multiple removablehydrogen-rechargeable power generators each has its own hydrogen storageand has a shape corresponding to a form factor of primary alkaline orlithium batteries; a vacuum pump coupled to the power generator manifoldto evacuate the multiple removable hydrogen-rechargeable powergenerators prior to providing hydrogen to the removablehydrogen-rechargeable power generators; a vacuum valve coupled to thepower generator manifold between the vacuum pump and the input of thepower generator manifold; and a controller adapted to control the vacuumpump, to control each power generator manifold valve, and to control thevacuum valve, the controller including: an internal fuel cell coupled toreceive generated hydrogen and to provide power to the controller; and arechargeable battery coupled to the internal fuel cell.
 13. Therecharger of claim 12, and further including the hydrogen generatingmodule that further includes a plurality of replaceable fuel sourcemodules, each fuel source module including an independently actuatedfuel source valve, wherein the controller further controls eachindependently actuated fuel source valve.
 14. The recharger of claim 13,further including: a hydrogen pump controlled by the controller andcoupled to the hydrogen generating module and to the first powergenerator manifold; and a fuel source manifold coupled to thehydrogen-generating module and to the hydrogen pump.
 15. The rechargerof claim 1, further including a pressure sensor coupled to the manifoldto provide pressure data to the control electronics, the pressure datarepresentative of a negative vacuum pressure and of a positivehydrogen-filling pressure.
 16. The recharger of claim 15, wherein thecontrol electronics, pressure sensor, and each independently actuatedvalve within the manifold are configured to: individually vacuum testthe multiple removable hydrogen-rechargeable power generators for damageby causing the vacuum pump to apply a vacuum while the pressure sensormonitors negative vacuum pressure; and individually pressure test themultiple removable hydrogen-rechargeable power generators for completionof hydrogen charging by causing the hydrogen pump to provide hydrogenwhile the pressure sensor monitors positive hydrogen pressure.